K-01 and K5-II Contrast AF problems

Started May 5, 2013 | Discussions thread
philzucker
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Re: K-01 and K5-II Contrast AF problems
In reply to MightyMike, May 5, 2013

MightyMike wrote:

I've been saying this for months... CDAF isn't the second coming of focusing systems, some lenses just don't work

Sigma 18-125mm F3.5-5.6, Sigma 75-200mm F3.8, Sigma 17-70mm F2.8-4.0, and others, the common issue is it gets worse at the tele end.

If my findings are correct add Tamron 18-250 f3.5-6.3 and Tamron 70-200 f2.8 to that list ... and yes, it's worse at the tele end with those two too ...

The issues is likely spherical aberrations, all lenses have this to some extent, this causes softening of the image if its really bad and allows for 3 points of focus, of course 2 of those points aren't accurate and one is best focus. What happens is the stupid CDAF system doesn't know which best focus to stop at and just lands on one. there may be a way the CDAF system can be programmed to go past the first point of focus to the best point of focus and this may be occurring in first party lenses.

Hmm, at least with the 70-200/f2.8 it's hard to for me to believe that severe aberrations are the problem here ... it's a very fine lens even wide open ... but of course I don't know for sure.

So for all those people who are singing the praises of CDAF being the most accurate system out their, look again, with some lenses and in low light its a dud! its useless!

Then again with other lenses and in good light it does have it's use, doesn't it?

Thanks for your info, Mike!

Phil

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